The invention relates to a mold part for the manufacture of molds for casting purposes by means of a molding substance, particularly to core boxes for the production of cores for casting purposes, wherein limited surface regions which are exposed to undue wear caused by the stream of the introduced molding substance, preferably surface regions in which the stream of molding substance moves at high velocity or while changing its direction relative to the mold surface and/or along the mold surface.
The term "mold part" in the sense of the invention includes a pattern as well as a core box.
The term "core" in the sense of the present invention includes, on the one hand, members which are placed into a casting mold and solve problems connected with cavities, undercuts and similar problem regions of casting mold design, i.e. casting cores in the conventional sense. On the other hand, the term also includes, in the sense of the present invention, components which can be combined to form a complete casting mold and are manufactured of the same molding substance and according to the same method as casting molds. Depending on the shape of the casting to be produced, the inner wall as well as the outer wall of the casting may be defined by the core members combined into the casting mold. Particularly for the manufacture of complete casting molds composed of several parts made of core sand to which a binder has been added as it is customarily employed as the molding substance for cores, a molding process is advisably employed in which the binder for the core sand is not activated by temperature but by chemical-catalytic processes so that the molding substance hardens in the mold in a short period of time without an increase in temperature and can then be removed from the mold.
While cores in the classical sense, i.e. components produced according to the prior art method, are placed into a sand mold defining the external contour of the casting, "cores" produced according to the above-described method, which, when assembled, constitute the complete casting mold, i.e. the mold defining the interior and exterior contours of the casting, are geometrically very complicated structures which require correspondingly complicated and thus expensive core boxes for their manufacture, particularly since high demands are placed here on the precision of such core boxes. Since the above-described "cold" molding process with chemical-catalytic hardening of the molding substance still in the core box itself requires only a short period of dwell of the molding substance in the core box, a high throughput results which can be even further increased by increasing the fill velocity of the stream of molding material to be introduced into the core box. It has now been found that, with such increases in throughput, the service life of a core box, under consideration of predetermined dimensional tolerances, is noticeably limited. As soon as the tolerance limit is reached, the respective core box must be exchanged and replaced by a new core box, or at least by a reconditioned core box. Due to the complicated geometrical shapes involved, new manufacture as well as reconditioning of such a core box is expensive even if, for that reason, light metal alloys are employed as the material for the core box. The use of a more resistant material for the core box is also not possible for reasons of cost due to the poorer workability of the materials that would be applicable for this purpose.